1. Field of the Invention
The present invention relates to lithographic apparatus and methods.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacturing of integrated circuits (ICs). In such a case, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Conventional lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at once, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
A conventional lithographic apparatus includes a support constructed to support the abovementioned patterning device. The support generally includes a number of retractable pins, so-called R-pins, configured to push the patterning device somewhat upwardly from the support or to lower it down into the support during exchange thereof. Sideways of the support, two manipulators are provided, each with an end effector having a carrier configured to transport respective patterning devices to and from the retractable pins. Thus, it is possible to extend the pins upwardly, pick up a patterning device from the pins with one of the manipulators, move it to another station, meanwhile place a patterning device on the still extended pins with the other manipulator, and retract the pins in order to lower the patterning device in the support. Such construction/configuration, with the retractable pins and the two manipulators, however, is rather complex and expensive.
Furthermore, a lithographic apparatus generally includes a support constructed to support the abovementioned patterning device, and two vertically moveable manipulators attached to a turret (rotating table). The turret with the manipulators is mounted above the support. Each manipulator includes an end effector connected thereto having a carrier configured to pick up a respective patterning device directly from the support or to place it thereon, when, depending on the position of the turret, the respective manipulator is positioned above the support. Thus, it is possible to pick up a patterning device from the support with one of the manipulators, rotate the turret, and place a patterning device in the support with the other manipulator. The turret, however, incorporates large required strokes and may need a four-axis manipulator in order to transport the patterning devices to and from the turret. Exchanging a patterning device with such a construction/configuration may be time consuming if the manipulator is required.